feat: Add Element Call / MatrixRTC support

src/api/client/capabilities.rs

@@ -51,5 +51,16 @@ pub(crate) async fn get_capabilities_route(
 		json!({"enabled": services.config.forget_forced_upon_leave}),
 	)?;
 
+	// MSC4143: MatrixRTC - advertise RTC transport support
+	if !services
+		.server
+		.config
+		.well_known
+		.rtc_transports
+		.is_empty()
+	{
+		capabilities.set("org.matrix.msc4143.rtc_foci", json!({"supported": true}))?;
+	}
+
 	Ok(get_capabilities::v3::Response { capabilities })
 }

src/api/client/well_known.rs

@@ -1,8 +1,6 @@
 use axum::{Json, extract::State, response::IntoResponse};
-use ruma::api::client::discovery::{
-	discover_homeserver::{self, HomeserverInfo},
-	discover_support::{self, Contact},
-};
+use ruma::api::client::discovery::discover_support::{self, Contact};
+use serde_json::{Value, json};
 use tuwunel_core::{Err, Result};
 
 use crate::Ruma;
@@ -10,20 +8,58 @@ use crate::Ruma;
 /// # `GET /.well-known/matrix/client`
 ///
 /// Returns the .well-known URL if it is configured, otherwise returns 404.
+/// Also includes RTC transport configuration for Element Call (MSC4143).
 pub(crate) async fn well_known_client(
 	State(services): State<crate::State>,
-	_body: Ruma<discover_homeserver::Request>,
-) -> Result<discover_homeserver::Response> {
+) -> Result<Json<Value>> {
 	let client_url = match services.server.config.well_known.client.as_ref() {
 		| Some(url) => url.to_string(),
 		| None => return Err!(Request(NotFound("Not found."))),
 	};
 
-	Ok(discover_homeserver::Response {
-		homeserver: HomeserverInfo { base_url: client_url },
-		identity_server: None,
-		tile_server: None,
-	})
+	let mut response = json!({
+		"m.homeserver": {
+			"base_url": client_url
+		}
+	});
+
+	// Add RTC transport configuration if available (MSC4143 / Element Call)
+	// Element Call has evolved through several versions with different field
+	// expectations
+	if !services
+		.server
+		.config
+		.well_known
+		.rtc_transports
+		.is_empty()
+	{
+		if let Some(obj) = response.as_object_mut() {
+			// Element Call expects "org.matrix.msc4143.rtc_foci" (not rtc_foci_preferred)
+			// with an array of transport objects
+			obj.insert(
+				"org.matrix.msc4143.rtc_foci".to_owned(),
+				json!(services.server.config.well_known.rtc_transports),
+			);
+
+			// Also add the LiveKit URL directly for backward compatibility
+			if let Some(first_transport) = services
+				.server
+				.config
+				.well_known
+				.rtc_transports
+				.first()
+			{
+				if let Some(livekit_url) = first_transport.get("livekit_service_url") {
+					obj.insert(
+						"org.matrix.msc4143.livekit_service_url".to_owned(),
+						livekit_url.clone(),
+					);
+				}
+			}
+		}
+	}
+
+	Ok(Json(response))
 }
 
 /// # `GET /.well-known/matrix/support`

src/api/router.rs

@@ -190,7 +190,8 @@ pub fn build(router: Router<State>, server: &Server) -> Router<State> {
 			get(client::get_room_summary_legacy)
 		)
 		.ruma_route(&client::well_known_support)
-		.ruma_route(&client::well_known_client)
+		// this is the only thing currently needed to support Element Video Rooms / Calls.
+		.route("/.well-known/matrix/client", get(client::well_known_client))
 		.route("/_tuwunel/server_version", get(client::tuwunel_server_version))
 		.ruma_route(&client::room_initial_sync_route)
 		.route("/client/server.json", get(client::syncv3_client_server_json));

src/core/config/mod.rs

@@ -2146,6 +2146,26 @@ pub struct WellKnownConfig {
 	///
 	/// example "@admin:example.com"
 	pub support_mxid: Option<OwnedUserId>,
+
+	/// Element Call / MatrixRTC configuration (MSC4143).
+	/// Configures the LiveKit SFU server for voice/video calls.
+	///
+	/// Requires a LiveKit server with JWT authentication.
+	/// The `livekit_service_url` should point to your LiveKit JWT endpoint.
+	///
+	/// Note: You must also set `client` above to your homeserver URL.
+	///
+	/// Example:
+	/// ```toml
+	/// [global.well_known]
+	/// client = "https://matrix.yourdomain.com"
+	///
+	/// [[global.well_known.rtc_transports]]
+	/// type = "livekit"
+	/// livekit_service_url = "https://livekit.yourdomain.com"
+	/// ```
+	#[serde(default)]
+	pub rtc_transports: Vec<serde_json::Value>,
 }
 
 #[derive(Clone, Copy, Debug, Deserialize, Default)]

tuwunel-example.toml

@@ -1832,6 +1832,26 @@
 #
 #support_mxid =
 
+# Element Call / MatrixRTC configuration (MSC4143).
+# Configures the LiveKit SFU server for voice/video calls.
+#
+# Requires a LiveKit server with JWT authentication.
+# The `livekit_service_url` should point to your LiveKit JWT endpoint.
+#
+# Note: You must also set `client` above to your homeserver URL.
+#
+# Example:
+# ```toml
+# [global.well_known]
+# client = "https://matrix.yourdomain.com"
+#
+# [[global.well_known.rtc_transports]]
+# type = "livekit"
+# livekit_service_url = "https://livekit.yourdomain.com"
+# ```
+#
+#rtc_transports = false
+
 #[global.blurhashing]
 
 # blurhashing x component, 4 is recommended by https://blurha.sh/